Oil Pump

ABSTRACT

An oil pump includes an inner rotor, an outer rotor, an outer ring, and a pump housing including a suction port and a discharge port, and including a first seal land formed between a terminal end section of the suction port and a start end section of the discharge port, and moreover including a rotor chamber that houses the inner rotor, the outer rotor, and the outer ring. In swing of an angle from an initial position to a final position of the outer ring, a final position eccentric axis connecting a rotation center of the inner rotor and a rotation center of the outer rotor is turnable in an area of an angle exceeding 90 degrees on the suction port side with respect to an initial position eccentric axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a discharge amount variable oil pumpmounted on a vehicle engine or the like, the oil pump being capable offurther increasing a discharge amount variable rate and further reducingunnecessary work in the engine and the pump, thereby improving fuelefficiency.

2. Description of the Related Art

There have been various discharge amount variable oil pumps. Among theoil pumps, there is an oil pump including a rotor of an inscribed type.In general, in an inscribed gear type oil pump, an inner rotor includingexternal teeth and an outer rotor including inner teeth rotate whilemeshing with each other. Spaces called cells are formed between theteeth of the inner rotor and the teeth of the outer rotor.

In the rotating motion of the inner rotor and the outer rotor, while arotation angle is in a range of 180 degrees of 360 degrees, the oil pumpsucks oil according to an increase in the volume of the cells. While therotation angle is in the remaining range of 180 degrees, the oil pumpdischarges the oil according to a decrease in the volume of the cells.In a normal inscribed teeth oil pump, which is not the variable capacitytype, a suction port is arranged in a phase where the volume of thecells increases and a discharge port is arranged in a phase where thevolume of the cells decreases.

In the discharge amount variable oil pump, in order to move the outerrotor along a predetermined track, an adjusting member is provided. Theouter rotor is turnably amounted on the adjusting member. A rotationcenter of the outer rotor is moved by swinging the adjusting member. Asthe oil pump of this type, there are oil pumps disclosed inWO2010/013625, Japanese Patent Application Laid-Open No. H10-169571,Japanese Patent Application Laid-Open No. H08-159046, and JapanesePatent Application Laid-Open No. 2008-298026.

Specifically, paragraph 0006 of WO2010/013625 mentions that “A lockerlever that actuates the adjustment ring 14 is swingably supported in thecasing portion 1. By swinging the locker lever, a rotation axis of theouter rotor 4 moves 90 degrees in a direction on the opposite side ofthe inner rotor 3 in a state in which the inner side row of teeth 24′and the outer side row of teeth 24 mesh with each other. Due to thismovement, a positional relation between the low pressure port 8 and thehigh pressure port 9 with respect to the ring gear set 5 of the innerrotor 3 and the outer rotor 4 changes to make it possible to adjust adischarge amount of the pump from a maximum discharge amount to zero.”

Paragraph 0037 of Japanese Patent Application Laid-Open No. H10-169571mentions that “The adjustment ring 14 rotates in the rotating directionD of the inner rotor 3 by a relatively small angle γ in a state in whichthe two rows of teeth 24 and 24′ of the adjustment gear 20 arecontinuously meshed with each other. Consequently, when the root circle15 of the adjustment ring 14 and the root circle 16 of the inner siderow of teeth 24′ rotate with respect to each other without slipping,first, the rotation axis of the outer rotor moves 90 degrees from aposition shown in FIG. 1A to a position shown in FIG. 1B around therotation axis of the inner rotor 3 in a direction opposite to a rotatingposition of the inner rotor 3. The position shown in FIG. 1B is a zeroposition of the pump. In an ideal case, fluid is not discharged in thisposition. In the zero position, the groove ports 8 and 9 extendsymmetrically on both sides of complete and open meshing positions.”

Paragraph 0023 of Japanese Patent Application Laid-Open No. H08-159046mentions that “According to such swing movement of the cam ring 5, arotation center position of the outer rotor 4 rotatably held in the camring 5 revolves 90 degrees in the clockwise direction with the teethheight of the inscribed gear pump set as a revolving diameter and withthe rotation center position of the inner rotor 3 set as a revolvingcenter. The capacity of the oil transfer reservoir section 11 on theterminal end vicinity 22 of the suction region 21 is minimized.”

Paragraph 0055 of Japanese Patent Application Laid-Open No. 2008-298026mentions that “When the pump revolution rate further rises, the pumpdischarge pressure acting on the adjustment ring 7 further increases.Therefore, as shown in FIG. 11, the adjustment ring 7 further rotates inthe counterclockwise direction and rotates to an angle of approximately30 degrees resisting a spring force of the spring member 27.

Therefore, the center point E of the outer rotor 5 moves approximately90 degrees. An eccentric direction from the inner rotor 4 is in an angleposition of approximately 90 degrees. Therefore, the capacity of thepump chamber 10 is substantially equal when the pump chamber 10 passesthe seal land section 15 from the suction chamber 11 to the dischargechamber 12 and when the pump chamber 10 passes the seal land section 16from the discharge chamber 12 to the suction chamber 11. A pumpdischarge amount is minimized.”

WO2010/013625 to Japanese Patent Application Laid-Open No. 2008-298026disclose an operation explained below in order to change a dischargecapacity of the oil pump. FIGS. 6A and 6B are schematic diagrams forexplaining the contents of WO2010/013625 to Japanese Patent ApplicationLaid-Open No. 2008-298026. When the discharge capacity of the oil pumpis maximized, a suction port “a” is arranged in a phase where the volumeof the cells increases and a discharge port “b” is arranged in a phasewhere the volume of the cells decreases. The position of an outer rotor“c” in this case is set as an initial position (see FIG. 6A). Aneccentric axis k at this point is perpendicular in FIG. 6A.

The eccentric axis k in a final position is tilted an angle θ₀ withrespect to the eccentric axis k in the initial position. A position ofthe eccentric axis k tilted 90 degrees is set as the final position ofthe outer rotor “c”. A suction amount and a discharge amount of a movingcell are substantially equal on the insides of both of the dischargeport “b” and the suction port “a”. Therefore, a suction amount and adischarge amount are offset and oil does not flow. Consequently, thedischarge capacity can be theoretically reduced to zero. As explainedabove, in WO2010/013625 to Japanese Patent Application Laid-Open No.2008-298026, when the discharge capacity of the oil pump istheoretically reduced to zero, it is a technical common sense to tiltthe eccentric axis k 90 degrees (see FIG. 6B).

That is, in WO2010/013625 to Japanese Patent Application Laid-Open No.2008-298026, when the eccentric axis k tilts 90 degrees with respect tothe initial position, according to the rotation by an inner rotor “d”and the outer rotor “c”, a sucking amount and a discharging amount ofthe passing oil in the cell are substantially equal on the insides ofthe discharge port “b” and the suction port “a”. That is, a suctionamount and a discharge amount of the oil by the cell are substantiallyequal and offset. The oil stops flowing.

However, when the applicant actually tilted the eccentric axis 90degrees and conducted an experiment, a result indicating that the oil ofapproximately 25% flowed with respect to a maximum discharge amount wasobtained. Therefore, a variable rate of a discharge amount is 75% and isnot zero. This means that improvement of fuel efficiency decreasesbecause variable width of the discharge capacity decreases.

As explained above, there is a cause that the discharge capacity of theoil pump cannot actually be reduced to zero even if the eccentric axis kis tilted 90 degrees. This cause is explained below. First, in the pump,the oil in a flowing state is always about to continue to flow in aforward direction from a suction side to a discharge side. If the enginecontinues to be operated, the oil necessarily flows in the forwarddirection.

The oil has mass. The oil flowing in the forward direction in the pumpmaintains a flowing state in the forward direction with the inertia ofthe oil. Even if action in a backflow direction occurs in the pump (whenthe eccentric axis exceeds 90 degrees), if the action is very small, theoil continues to flow in the forward direction without changing theflowing direction. Therefore, even if the eccentric axis k is turned 90degrees, although the discharge amount decreases, the flow of the oil inthe forward direction does not decrease to zero. The oil discharge ofthe pump is continued.

As an example of the cause that the discharge capacity of the oil pumpdoes not decrease to zero even if the eccentric axis k is tilted 90degrees, there is cavitation that occurs in the pump. When the eccentricaxis k turns 90 degrees, the arrangement changes to arrangement shown inFIG. 6B. A configuration shown in FIG. 6B is vertically symmetric withrespect to the eccentric axis k.

In a state in which the eccentric axis k turns 90 degrees and isarranged horizontally (see FIG. 6B), seal lands (partitioning sections)are arranged on both upper and lower side with respect to the eccentricaxis k. When the inner rotor and the outer rotor rotatescounterclockwise in such a state, a discharge operation is performed ona side below the eccentric axis k horizontally arranged on the dischargeport “b” side of the pump because the volume of the cells graduallydecreases. A suction operation is performed on a side above theeccentric axis k because the volume of the cells gradually increases.

In this case, in a process in which the volume of the cells decreases,the oil is surely discharged by the decrease in the volume of the cells.That is, in the discharge port “b”, in a contraction process of the cellthat moves counterclockwise, the oil in the cell is substantiallycompletely discharged. On the other hand, in an expansion process of thecell that moves counterclockwise in the discharge port “b”, the oil issometimes not sufficiently filled in the cell having increased volume.In particular, as rotation speed of the rotors increases, an air gapportion not filled with the oil tends to occur in a part of the cell.

Further, while the volume of the cell that move counterclockwisecontinues to increase, when a part of the cell reaches the seal landwhere the oil is absent, the cell cannot suck the oil and a vacuum areaoccurs in the cell. In this way, in particular, when the cell moveswhile increasing the volume rapidly, inflow of the oil less easilyperformed and the vacuum area increases. As a result, a large number ofair bubbles (very small vacuum bubbles) are generated from the oil inthe cell.

This phenomenon is so-called cavitation. Even if a part of the cell ispresent in the discharge port “b”, the cell cannot suck the oil becauseof the large number of air bubbles. In particular, probability ofcavitation occurrence increases when the cell starts to cross the sealland section and, in addition, the volume of the cell increases.

Therefore, in the related art, in a state in which the eccentric axis kturns 90 degrees, on the discharge port “b” side, an oil dischargeamount by the cell is larger than a suction amount in an oil dischargeoperation of the cell in which the volume decreases and an oil suctionoperation of the cell in which the volume increases. As a result, adischarge amount and a suction amount of the oil in the discharge port“b” are not equal and are not fully offset.

Moreover, since the discharge amount of the oil by the cell in thedischarge port “b” is larger than the suction amount, even if theeccentric axis k turns 90 degrees, an oil discharge amount decreases asa whole. The oil continues to flow in the forward direction. The flowdoes not stop. An expected variable rate of the discharge amount cannotbe expected. Therefore, it is an object of the present invention (atechnical problem to be solved) to further increase the variable rate ofthe discharge amount in an operation for rotating the eccentric axis andchanging the discharge amount.

SUMMARY OF THE INVENTION

Therefore, the inventor earnestly carried out researches in order tosolve the problems and solved the problems according to embodiments ofthe present invention explained below.

According to a first aspect of the present invention, there is providedan oil pump including: an inner rotor including outer teeth; an outerrotor including inner teeth that form, together with the outer teeth,cells, and rotating while having a predetermined eccentricity amountwith respect to a rotation center of the inner rotor; an outer ring thatswings, with respect to a rotation center of the inner rotor, a rotationcenter of the outer rotor along a track circle having the eccentricityamount as a radius; and a pump housing including a suction port and adischarge port, and including a first seal land formed between aterminal end section of the suction port and a start end section of thedischarge port, and moreover including a rotor chamber that houses theinner rotor, the outer rotor, and the outer ring. In swing of an anglefrom an initial position to a final position of the outer ring, a finalposition eccentric axis connecting the rotation center of the innerrotor and the rotation center of the outer rotor is turnable in an areaof an angle exceeding 90 degrees on the suction port side with respectto an initial position eccentric axis.

According to a second embodiment of the present invention, in the oilpump according to the first embodiment, in the swing from the initialposition to the final position of the outer ring, the final positioneccentric axis connecting the rotation center of the inner rotor and therotation center of the outer rotor is turnable in an area of an angleexceeding 90 degrees to an angle of 150 degrees on the suction port sidewith respect to the initial position eccentric axis.

According to a third embodiment of the present invention, in the oilpump according to the first embodiment, in the swing from the initialposition to the final position of the outer ring, the final positioneccentric axis connecting the rotation center of the inner rotor and therotation center of the outer rotor is turnable in an area of an angle of100 degrees to 140 degrees on the suction port side with respect to theinitial position eccentric axis.

In the present invention, in the swing from the initial position to thefinal position of the outer ring, the final position eccentric axisconnecting the rotation center of the inner rotor and the rotationcenter of the outer rotor is turnable in the area of the angle exceeding90 degrees to the suction port side with respect to the initial positioneccentric axis. Therefore, when the eccentric axis of the inner rotorand the outer rotor is the final position eccentric axis, it is possibleto further reduce the discharge amount and increase the variable rate ofthe discharge capacity to approximately 80% or more. Therefore, it ispossible to reduce useless work of the pump and improve fuel efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a main part enlarged sectional view showing an initialposition of an outer ring, an outer rotor, and an inner rotor of thepresent invention;

FIG. 1B is an enlarged view showing the configuration in the vicinity ofa fan-shaped turning track;

FIG. 2 is a main part enlarged sectional view showing a final positionof the outer ring, the outer rotor, and the inner rotor of the presentinvention;

FIG. 3 is a schematic diagram showing a configuration in the presentinvention;

FIG. 4 is a graph showing characteristics of the present invention andthe related art;

FIG. 5A is a main part enlarged sectional view of a state in which aphase of the outer rotor of the present invention is rotated 90 degreesin a clockwise direction with respect to an initial position eccentricaxis;

FIG. 5B is a view of a state in which the inner rotor and the outerrotor turn by a small angle in the state shown in FIG. 5A;

FIG. 5C is an “α” part enlarged view of FIG. 5B;

FIG. 6A is a schematic diagram showing an initial position state of theouter rotor in the related art; and

FIG. 6B is a schematic diagram showing a final position state of theouter rotor in the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is explained below with referenceto the drawings. An oil pump according to the embodiment of the presentinvention mainly includes, as shown in FIGS. 1A to 3, a pump housing A,an inner rotor 3, an outer rotor 4, an outer ring 5, and an operationunit 9. In the pump housing A, a rotor chamber 1 is formed. In a bottomsurface section of the rotor chamber 1, a shaft hole 11, into which adriving shaft for pump driving is inserted, is formed. A suction port 12and a discharge port 13 are formed around the shaft hole 11. Seal landsare formed between the suction port 12 and the discharge port 13.

The seal lands are formed in two places in the rotor chamber 1. One ofthe seal lands is located between a terminal end section 12 b of thesuction port 12 and a start end section 13 a of the discharge port 13.The seal land is referred to as first seal land 14.

The other seal land is located between a terminal end section 13 b ofthe discharge port 13 and a start end section 12 a of the suction port12. The seal land is referred to as second seal land 15. In the pumphousing A, an operation chamber 2 leading to the rotor chamber 1 isformed and an operation projecting section 51 of the outer ring 5 (to bedescribed later) is arranged. The inner rotor 3, the outer rotor 4, andthe outer ring 5 are internally mounted in the rotor chamber 1.

The inner rotor 3 is a gear formed in a trochoid shape or asubstantially trochoid shape. A plurality of outer teeth 31 are formedin the inner rotor 3 (see FIGS. 1A to 3). A boss hole 32 for the drivingshaft is formed in a center position in the diameter direction of theinner rotor 3. A driving shaft 33 is pierced through and fixed in theboss hole 32. The boss hole 32 is formed in a non-circular shape. Thedriving shaft is fixed to the inner rotor 3 by press-fitting of a shaftfixing section having substantially the same shape as the boss hole 32or by fixing means having width across flat or the like. The inner rotor3 rotates according to rotation driving of the driving shaft.

The outer rotor 4 is formed in an annular shape. A plurality of innerteeth 41 are formed on the inner circumferential side of the outer rotor4. The number of the outer teeth 31 of the inner rotor 3 is smaller thanthe number of the inner teeth 41 of the outer rotor 4 by one. Aplurality of cells (inter-teeth spaces) S are formed by the outer teeth31 of the inner rotor 3 and the inner teeth 41 of the outer rotor 4.

A rotation center of the inner rotor 3 is represented as Pa. Theposition of the rotation center Pa is immobile with respect to the rotorchamber 1. A rotation center of the outer rotor 4 is represented as Pb.An imaginary line connecting the rotation center Pa and the rotationcenter Pb is referred to as eccentric axis. As the eccentric axis, aninitial position eccentric axis La and a final position eccentric axisLx are present according to the positions of the outer rotor 4 and theouter ring 5.

A distance between the rotation center Pa of the inner rotor 3 and therotation center Pb of the outer rotor 4 is referred to as eccentricityamount e. A track circle having the rotation center Pa of the innerrotor 3 as a center and having the eccentricity amount e as a radius isformed. According to operation of the outer ring 5, the rotation centerPb of the outer rotor 4 moves along a fan-shaped arc, which is a portionof the track circle, from an initial position state to a final positionstate (see FIG. 1B). An arc-shaped track portion of the rotation centerPb in this case is referred to as fan-shaped turning track Q.

The outer ring 5 is formed in a substantially annular shape. Theoperation projecting section 51 formed to project outward in thediameter direction from a predetermined place of an outercircumferential side surface 5 a of the outer ring is provided. Awrapping inner circumference section 52 functioning as a roundthrough-hole is formed on the inward side of the outer ring 5. The outerring 5 is swung in the rotor chamber 1 by the operation unit 9 (to bedescribed later) via the operation projecting section 51. The operationprojecting section 51 is arranged in the operation chamber 2 and canswing in the operation chamber 2.

The wrapping inner circumference section 52 is formed as a circularinner wall surface. The inner diameter of the wrapping innercircumference section 52 is substantially the same as the outer diameterof the outer rotor 4. Specifically, the inner diameter of the wrappinginner circumference section 52 is slightly larger than the outerdiameter of the outer rotor 4. The outer rotor 4 is inserted into thewrapping inner circumference section 52 with a clearance providedbetween the wrapping inner circumference section 52 and the outer rotor4 such that the outer rotor 4 is smoothly rotatable.

The position of a diameter center Pc of the wrapping inner circumferencesection 52 of the outer ring 5 coincides with the position of therotation center Pb of the outer rotor inserted into the wrapping innercircumference section 52 (see FIG. 2). The outer ring 5 is arranged inthe rotor chamber 1. The outer rotor 4 is arranged in the wrapping innercircumference section 52 to rotatably support the outer rotor 4 andswing the outer rotor 4 along the fan-shaped turning track Q via theoperation unit 9 (see FIGS. 1A to 2).

The outer ring 5 is internally mounted in the rotor chamber 1 of thepump housing A. The outer ring 5 is swingable in the rotor chamber 1.Therefore, the rotor chamber 1 is formed slightly wider than theexternal shape of the outer ring 5. A space for the outer rotor 4 toswing is provided in addition. The outer ring 5 is swung by theoperation unit 9. However, a track of the swing is determined. Thediameter center Pc of the wrapping inner circumference section 52 swingsalong the fan-shaped turning track Q.

In the present invention, an initial position and a final position arepresent for the inner rotor 3 and the outer rotor 4. The initialposition refers to a position of the inner rotor 3, the outer rotor 4,and the outer ring 5 at the time when a largest cell Sa having a largestcapacity among the plurality of cells S formed by the inner rotor 3 andthe outer rotor 4 is located on the first seal land 14. In the initialposition, the number of revolutions of the engine is mainly in a lowrevolution area. An eccentric axis connecting the rotation center Pa ofthe inner rotor 3 and the rotation center Pb of the outer rotor 4 in theinitial position is referred to as initial position eccentric axis La(see FIG. 1A).

The final position refers to a position of the outer ring 5, the innerrotor 3, and the outer rotor 4 at the time when the outer ring 5 swingsfrom the initial position to the maximum, the rotation center Pb of theouter rotor 4 moves on the fan-shaped turning track Q, and the positionof the largest cell Sa moves to the maximum. The number of revolutionsof the engine is in a medium revolution area and a high revolution area.An eccentric axis connecting the rotation center Pa of the inner rotor 3and the rotation center Pb of the outer rotor 4 in the final position isreferred to as final position eccentric axis Lx (see FIG. 2).

An angle of swing from the initial position eccentric axis La to thefinal position eccentric axis Lx of the outer rotor 4 actually swung bythe outer ring 5 is represented as θ and an angle of swing of theoperation projecting section 51 of the outer ring 5 at this point isrepresented as θa. The angle θa is markedly smaller than the angle θ.

That is, only by slightly swinging the operation projecting section 51of the outer ring 5 with the operation unit 9, a maximum swing angle ofthe outer rotor 4, that is, an angle formed by the initial positioneccentric axis La and the final position eccentric axis Lx can be setextremely large. Specifically, when a swing angle of the operationprojecting section 51 can be set to approximately 15 degrees, the angleformed by the initial position eccentric axis La and the final positioneccentric axis Lx of the outer rotor 4 can be set to approximately 120degrees (see FIGS. 1A and 2).

When the outer ring 5 actually swings from the initial position to thefinal position, the eccentric axis swings in an area of the angle θformed by the initial position eccentric axis La and the final positioneccentric axis Lx. In this way, the eccentric axis swings in the area ofthe angle θ. The angle θ is an angle exceeding 90 degrees. That is, theangle θ does not include 90 degrees. Therefore, the angle θ formed bythe initial position eccentric axis La and the final position eccentricaxis Lx is an obtuse angle.

As a range of the angle θ, the angle θ exceeds 90 degrees and is equalto or smaller than approximately 150 degrees. In this embodiment, whenthe angle θ of the final position eccentric axis Lx is approximately 150degrees with respect to the initial position eccentric axis La, thelargest cell Sa is present within an area of the suction port 12. Therange of the angle θ is sometimes limited to enable the final positioneccentric axis Lx to turn in an area of an angle of approximately 100degrees to approximately 140 degrees on the suction port 12 side withrespect to the initial position eccentric axis La. In the presentinvention, an optimum angle θ of the final position eccentric axis Lxwith respect to the initial position eccentric axis La is set toapproximately 120 degrees. Consequently, the oil pump of the presentinvention operates as explained below.

First, the oil pump sucks the oil a little from the start end section 12a side of the suction port 12. When the cell S passes a position of thelargest cell Sa, the oil pump discharges a large amount of the oil tothe inside of the suction port 12. The oil pump discharges the oil alittle between a position close to the start end section 13 a side ofthe discharge port 13 and a position where the cell S is the smallestcell Sb. When the oil passes this position, the oil pump sucks a largeamount of the oil from the discharge port 13. As a discharge amount, theoil equal to or smaller than 20% of a maximum discharge amount flows inthe forward direction. Consequently, it is possible to set the variablerate to approximately 80% or higher (see FIG. 4).

In the operation projecting section 51 of the outer ring 5, a firstpressure receiving surface 51 a is formed in one side of a swingingdirection and a second pressure receiving surface 51 b is formed on theother side. An elastic pressing section 8 provided in the operationchamber 2 elastically presses the second pressure receiving surface 51 band generates a load for always setting the outer ring 5 and the outerrotor 4 in the initial position.

A first oil path 21 and a second oil path 22 are provided between theoperation unit 9 and the operation chamber 2. Hydraulic pressures can berespectively applied to the first pressure receiving surface 51 a andthe second pressure receiving surface 51 b of the operation projectingsection 51 in the operation chamber 2 by the operation unit 9. Theoperation projecting section 51 is swung by hydraulic pressure controlof the operation unit 9 according to a pressure difference between thehydraulic pressures applied to the first pressure receiving surface 51 aand the second pressure receiving surface 51 b of the operationprojecting section 51 and an elastic pressing force of the elasticpressing section 8. Consequently, the operation unit 9 swings the outerring 5 (see FIGS. 1A to 3).

An operation for guiding the swing of the outer ring 5 is performed by aplurality of tooth mark sections 6 provided between the rotor chamber 1and the outer ring 5. The tooth mark sections 6 include outer sideposition tooth marks 6 b formed in the rotor chamber 1 and inner sideposition tooth marks 6 a formed on the outer circumferential sidesurface of the outer ring 5. As the operation unit 9 for the outer ring5, specifically, a solenoid valve or the like is used. In the figure,reference numeral 7 denotes seal sections, which play a role of shuttingoff a space between the rotor chamber 1 and the outer ring 5.

FIG. 5A shows a state in which, in the present invention, an eccentricaxis Lm connecting the rotation center Pa of the inner rotor 3 and therotation center Pb of the outer rotor 4 moves 90 degrees in theclockwise direction with respect to the initial position eccentric axisLa and a phase of the outer rotor 4 shifts. In this case, naturally, theposition of the diameter center Pc of the wrapping inner circumferencesection 52 of the outer ring 5 and the position of the rotation centerPb of the outer rotor 4 coincide with each other. According to the shiftof the phase, the largest cell Sa crosses the initial position eccentricaxis La on the eccentric axis Lm that moves in the clockwise direction(see FIG. 5A).

Immediately after the start of the engine, first, as shown in FIG. 1A,the rotation center Pb of the outer rotor 4 is in the position of theinitial state and largest cell Sa crosses the initial position eccentricaxis La on the initial position eccentric axis La. In this case, the oilflows in the forward direction from the suction port 12 to the dischargeport 13. The flow of the oil in the forward direction is maintained evenif the eccentric axis Lm moves 90 degrees in the clockwise directionwith respect to the initial position eccentric axis La.

That is, since the oil has mass, the oil is about to continue to flow inthe forward direction with the inertia of the oil. The oil has power toflow in the forward direction. When the phase of the outer rotor 4shifts and the cell S performs operations for discharging and suckingthe oil within the range of the discharge port 13, the power is added tothe discharge operation, a discharge amount of the oil exceeds a suctionamount, and, eventually, the flow in the forward direction of the oil ismaintained.

As the eccentric axis Lm approaches the final position eccentric axisLx, contraction of the volume of the cell S within the range of thedischarge port 13 disappears, the discharge of the oil is stopped, and,on the contrary, expansion of the volume of the cell S increases, andonly suction of the oil is performed. Therefore, a backflow of a part ofthe oil from the discharge port 13 to the suction port occurs. There isno flow in the forward direction at a predetermined angle exceeding 90degrees.

The operation explained above can also be explained by application ofoccurrence of cavitation (see FIGS. 5B and 5C). That is, when theeccentric axis Lm turns 90 degrees and the phase of the outer rotor 4shifts, the inner rotor 3 and the outer rotor 4 become verticallysymmetrical with respect to the eccentric axis Lm. The first seal land14 and the second seal land 15 are arranged on both upper and lowersides of the eccentric axis Lm.

The inner rotor 3 and the outer rotor 4 rotate counterclockwise, wherebythe volume of the cell S gradually decreases and the oil is dischargedon a side below the eccentric axis Lm horizontally arranged within therange of the discharge port 13. The volume of the cell S graduallyincreases and the oil is sucked on a side above the eccentric axis Lm(see (α) of FIG. 5B).

In this case, in a process in which the volume of the cell S decreases,the oil is surely discharged by a reduced amount of the volume of thecell S. However, in a process in which the volume of the cell Sincreases and the oil is about to be sucked, the oil is not sufficientlyfilled in the cell S. In particular, as the rotating speed of the rotorsincreases, an air gap portion not filled with the oil tends to occur ina part of the cell S.

Further, while the volume of the cell S moving counterclockwiseincreases, when the cell S starts to cross the second seal land 15 wherethe oil is absent, the cell S cannot sufficiently absorb the oil. Avacuum area occurs in the cell S. As the cell S moves, the vacuum areacontinues to increase and a large number of air bubbles q, that is,cavitation occurs (see FIG. 5C).

When a crossing portion of the cell S and the second seal land 15further increases, a larger number of air bubbles q occur. Even if anegative pressure in the cell S increases, the large number of airbubbles q prevent suction of the oil and oil suction of the cell Sdecreases. Consequently, within the range of the discharge port 13, anoil discharge amount by the cell S exceeds a suction amount or only adischarging operation is performed and the flow of the oil in theforward direction is maintained.

Although the flow of the oil in the forward direction is maintained, atotal discharge amount of the pump decreases. As a result, the eccentricaxis Lm is turned exceeding 90 degrees with respect to the initialposition eccentric axis La. Therefore, a turning range of the eccentricaxis Lm in which the discharge amount can be further reduced increases.It is possible to obtain a large variable rate.

In the second embodiment, in the swing of the outer ring from theinitial position to the final position, the final position eccentricaxis connecting the rotation center of the inner rotor and the rotationcenter of the outer rotor is turnable in the area of the angle exceeding90 degrees to the angle of 150 degrees to the suction port side withrespect to the initial position eccentric axis. Therefore, in a processin which the engine changes from the low revolution area to the highrevolution area, a position change of the cell having the maximumcapacity from the initial position eccentric axis to the final positioneccentric axis is performed in the range of the angle exceeding 90degrees to 150 degrees. Consequently, it is possible to set the variablerate of the discharge amount of the oil higher than the variable rate inthe past. Further, it is possible to change the variable rate of thedischarge amount of the oil to a desired value by changing the turningangle of the outer ring.

In the third embodiment, in the swing from the initial position to thefinal position of the outer ring, the final position eccentric axisconnecting the rotation center of the inner rotor and the rotationcenter of the outer rotor is turnable in the area of the angle of 100degrees to 140 degrees to the suction port side with respect to theinitial position eccentric axis. Consequently, it is possible to highlyaccurately set the variable rate of the discharge amount of the oil.Further, it is possible to change the variable rate of the dischargeamount of the oil to a desired value by changing the turning angle ofthe outer ring.

What is claimed is:
 1. An oil pump comprising: an inner rotor includingouter teeth; an outer rotor including inner teeth that form, togetherwith the outer teeth, cells, and rotating while having a predeterminedeccentricity amount with respect to a rotation center of the innerrotor; an outer ring that swings, with respect to a rotation center ofthe inner rotor, a rotation center of the outer rotor along a trackcircle having the eccentricity amount as a radius; and a pump housingincluding a suction port and a discharge port, and including a firstseal land formed between a terminal end section of the suction port anda start end section of the discharge port, and moreover including arotor chamber that houses the inner rotor, the outer rotor, and theouter ring, wherein in swing of an angle from an initial position to afinal position of the outer ring, a final position eccentric axisconnecting the rotation center of the inner rotor and the rotationcenter of the outer rotor is turnable in an area of an angle exceeding90 degrees on the suction port side with respect to an initial positioneccentric axis.
 2. The oil pump according to claim 1, wherein, in theswing from the initial position to the final position of the outer ring,the final position eccentric axis connecting the rotation center of theinner rotor and the rotation center of the outer rotor is turnable in anarea of an angle exceeding 90 degrees to an angle of 150 degrees on thesuction port side with respect to the initial position eccentric axis.3. The oil pump according to claim 1, wherein, in the swing from theinitial position to the final position of the outer ring, the finalposition eccentric axis connecting the rotation center of the innerrotor and the rotation center of the outer rotor is turnable in an areaof an angle of 100 degrees to 140 degrees on the suction port side withrespect to the initial position eccentric axis.